1. Field of the Invention
This invention relates to a pressure pick-up especially for measuring the intake pressure of internal combustion engies, designed so as to facilitate the control of significant parameters. This design makes it possible either to accept wide ranges of differences in the physical and mechanical characteristics of the various pieces making up the pick-up for a given range of the functional electrical reading/pressure ratio, or simply to modify the functional ratio, at a low cost, without changing the definition of the various pieces used to make the pick-up.
2. Description of the Prior Art
The principle has long been known of a pressure pick-up or pressure variation pick-up in which a piece made of a magnetic material cooperates with a bobbin and follows the movements of a flexible membrane which covers a cavity subjected to pressure or change in pressure to be measured. Different modes of manufacture have been proposed on the basis of this principle.
It is known that, for various applications in automobile electronics, it is worthwhile to know with a high degree of precision the intake pressure of an internal combustion engine. Among such applications reference may be made to integral electronic ignition, electronic fuel injection, or gauges indicating economical driving.
In the case of electronic ignition, used here as an example of application, a problem arises if there is a desire to mount the same computer on a full line of vehicles, due to the fact that the cartography of the laws of ignition advance as a function of intake pressure varies from one type of vehicle to the next. In addition, the same problem arises on the same type of vehicle if there is a desire to modify slightly, without changing the computer, the law for adjusting the ignition advance as a function of ignition pressure either to take account of variations in the characteristics of the motor during its life or to take into account short-term or local changes in the composition of fuels. In order to reduce the cost of parts such as an electronic computer, therefore, it is widely known that there is an interest, on the one hand, in producing large volumes of identical parts and, on the other hand, in avoiding the need for storage, especially in the distribution network, of a large number of computers which are far more costly than pick-ups.
A further difficulty arises if the ignition advance law for a given engine must be defined with great precision, which is especially the case for those motors which have little protection from pinging for the law considered. This implies, usually with respect to the pressure parameter, the use of costly pick-ups.